Light Management of Metal Halide Scintillators for High-Resolution X-Ray Imaging

Temperature-Adaptive Organic Scintillators for X-ray Radiography

Organic phosphorescence or thermally activated delayed fluorescence (TADF) scintillators, while effective in utilizing triplet excitons, are sensitive to temperature changes, which can impact radioluminescence performance. In this study, we have developed a type of temperature-adaptive organic scintillator with phosphorescence and TADF dual emission. These scintillators can automatically switch modes with temperature changes, enabling efficient radioluminescence from 77 to 400 K. The highest photoluminescence quantum yield and light yield are 83.2% and 78,229 ± 562 photons MeV-1 excited by a UV lamp and X-ray, respectively. Their detection limit is 51 and 23 nGy·s-1 at room temperature and 77 K, respectively, which is lower than the standard dosage of 5.5 μGy s-1 for X-ray diagnostics. Moreover, given the high spatial resolution of 21.7 l p mm-1, we demonstrate their potential application in multiple-temperature X-ray radiography, offering promising new possibilities. This work opens a new route for developing organic scintillators to adapt to ambient temperature change and paves the way for their use in various temperature-sensitive radiography applications.

Molecular Engineering for High-Performance X-ray Scintillators

X-ray scintillators, materials that convert high-energy radiation into detectable light in the ultraviolet to visible spectrum, are widely used in industrial and medical applications. Organic and organic-inorganic hybrid systems have emerged as promising alternatives for X-ray detection and imaging due to their mechanical flexibility, lightweight, tunable excited states, and solution processability for large-scale fabrication. However, these systems often suffer from weak X-ray absorption and insufficient exciton utilization, which seriously affects their scintillation performance, limiting their potential for broader application and commercialization. This review highlights recent advances in molecular engineering for developing high-performance X-ray scintillators. It focuses on molecular design principles, such as the heavy atom effect, donor-acceptor/host-guest strategies, hydrogen/halogen bonding, molecular sensitization, and crystal packing, for enhancing scintillation performance. By leveraging these approaches, researchers have made significant strides in improving X-ray scintillation efficiency and advancing the potential of these materials for commercial applications.

Scintillating Glass Fiber Arrays Enable Remote Radiation Detection and Pixelated Imaging

The emerging metal halide perovskites are challenging the traditional scintillators in the field of radiation detection and radiography. However, they lack the capability for remote and real-time radiation monitoring and imaging in confined and hostile conditions. To address this issue, details on an inorganic scintillating glass fiber incorporating perovskite quantum dots (QDs) as highly efficient pixelated radiation emitters are reported, while the glass fibers themselves serve at the same time as low-loss waveguides, enabling long-distance and underwater X-ray detection. The multi-color emissions and controllable radiation sensitivities endow CsPbX3 (X = Cl, Br, I) QD scintillating glass fibers with the potential as wearable and visualized radiation indicators. Furthermore, these scintillating glass fibers can be regularly arranged into a fiber array plate with a thickness of 7.5 mm to enhance X-ray absorption for X-ray imaging. Leveraging the light-guiding character of glass fibers, a 5 × 5 fiber array with fiber lengths up to 11 cm has demonstrated the potential of remote pixelated X-ray imaging. This study offers a novel platform for the development of remote detectors and imagers for X-ray radiation.

Organic Manganese Halides with Near-Unity Quantum Efficiency for High-Resolution and Flexible X-Ray Detection and Imaging

In this paper, two new organic manganese halides (pe-ted)2MnX4 (pe-ted+ = ethylphenyltriethylenediamine cation, X = Cl, Br) are synthesized, exhibiting green luminescence with near-unity photoluminescence quantum efficiency. (pe-ted)2MnBr4 shows good linear response to X-ray dose rate, with a high light yield of ≈62 000 photons MeV-1 and low detection limit of 1.376 µGy s-1. Flexible scintillator film is prepared by blending with polydimethylsiloxane for high-resolution imaging, with a low detection limit (5.173 µGy s-1), an excellent X-ray imaging spatial resolution (18.0 lp mm-1) and an impressive X-ray irradiation switching stability (3.6 mGy s-1). WLED of high color rendering index has also been fabricated. These findings represent an example of shapeable X-ray scintillators, providing new possibilities for curved and 3D X-ray imaging.

Controlled Ligand-Free Growth of Free-Standing CsPbBr3 Perovskite Nanowires

Metal halide perovskite nanowires are widely studied due to their unique electronic and optical characteristics, making them promising for light emitting and detection applications. We developed a ligand-free method to grow vertically aligned free-standing CsPbBr3 nanowires from anodized aluminum oxide nanopore substrates. Here, we investigate the growth process using in situ microscopy with ultraviolet and visible light excitation, revealing a highly dynamic process with pronounced fluorescence at locations where high-density free-standing nanowires could be found. The yield of the growth is strongly improved by using a growth reactor with controlled N2 flow, increasing from 17 to 60%. We systematically investigated the growth dependence on the temperature and N2 flow rate and identified optimal parameters at 70 °C and 0.8 L/min, respectively. The improved control over the growth of free-standing nanowires expands opportunities for their integration into optoelectronic devices.

Micro/Nano Engineering Advances Next-Generation Flexible X-ray Detectors

The growing demands for X-ray imaging applications impose diverse and stringent requirements on advanced X-ray detectors. Among these, flexibility stands out as the most expected characteristic for next-generation X-ray detectors. Flexible X-ray detectors can spatially conform to nonflat surfaces, substantially improving the imaging resolution, reducing the X-ray exposure dosage, and enabling extended application opportunities that are hardly achievable by conventional rigid flat-panel detectors. Over the past years, indirect- and direct-conversion flexible X-ray detectors have made marvelous achievements. In particular, microscale and nanoscale engineering technologies play a pivotal role in defining the optical, electrical, and mechanical properties of flexible X-ray detectors. In this Perspective, we spotlight recent landmark advancements in flexible X-ray detectors from the aspects of micro/nano engineering strategies, which are broadly categorized into two prevailing modalities: materials-in-substrate and materials-on-substrate. We also discuss existing challenges hindering the development of flexible X-ray detectors, as well as prospective research opportunities to mitigate these issues.

Metal halide perovskite polymer composites for indirect X-ray detection

Metal halide perovskites (MHPs) have emerged as a promising class of materials for radiation detection due to their high atomic numbers and thus high radiation absorption, tunable and efficient luminescent properties and simple solution processability. Traditional MHP scintillators, however, suffer from environmental degradation, spurring interest in perovskite-polymer composites. This paper reviews recent developments in these composites tailored for scintillator applications. It discusses various synthesis methods, including solution-based and mechanochemical techniques, that enable the formation of composites with enhanced performance metrics such as light yield, detection limit, and environmental stability. The review also covers the remaining challenges and opportunities in fabrication techniques and performance metric evaluations of this class of materials. By offering a comprehensive overview of current research and future perspectives, this paper underscores the potential of perovskite-polymer composites to revolutionize the field of radiation detection.

Emerging Hybrid Metal Halide Glasses for Sensing and Displays

Glassy hybrid metal halides have emerged as promising materials in recent years due to their high structural adjustability and low melting points, offering unique merits that overcome the limitations of their crystalline and polycrystalline counterparts as well as other conventional amorphous semiconductors. This review article comprehensively explores the structural characteristics, electronic properties, and chemical coordination of hybrid metal halides, emphasizing their role in the glass transition from the crystalline phase to the amorphous phase. We examine the intrinsic disorder within the amorphous phase that facilitates light transmission and discuss recent advances in device architecture and interface engineering by optimizing the charge transport of glassy hybrid metal halides for high-quality applications. With full theoretical understanding and rational structural design, potential applications in displays, information storage, X-ray imaging, and sensing are highlighted, underscoring the transformative impact of glassy hybrid metal halides in the fields of materials science and information science.

A Thermo-Responsive MOFs for X-Ray Scintillator

Thermo-responsive smart materials have aroused extensive interest due to the particular significance of temperature sensing. Although various photoluminescent materials are explored in thermal detection, it is not applicable enough in X-ray radiation environment where the accuracy and reliability will be influenced. Here, a strategy is proposed by introducing the concept of radio-luminescent functional building units (RBUs) to construct thermo-responsive lanthanide metal-organic frameworks (Ln-MOFs) scintillators for self-calibrating thermometry. The rational designs of RBUs (including organic ligand and Tb3+/Eu3+) with appropriate energy levels lead to high-performance radio-luminescence. Ln-MOFs scintillators exhibit perfect linear response to X-ray, presenting low dose rate detection limit (min ≈156.1 nGyairs-1). Self-calibrating detection based on ratiometric XEL intensities is achieved with good absolute and relative sensitivities of 6.74 and 8.1%K-1, respectively. High relative light yield (max ≈39000 photons MeV-1), imaging spatial resolution (max ≈18 lp mm-1), irradiation stability (intensity ≈100% at 368 K in total dose up to 215 Gyair), and giant color transformation visualization benefit the applications, especially the in situ thermo-responsive X-ray imaging. Such strategy provides a promising way to develop the novel smart photonic materials with excellent scintillator performances.

Zero-Dimensional Copper(I) Halide Microcrystals as Highly Efficient Scintillators for Flexible X-ray Imaging

Commercially available rare-earth-doped inorganic oxide materials have been widely applied as X-ray scintillators, but the fragile characteristics, high detection limit, and harsh preparation condition seriously restrict their wide applications. Furthermore, it remains a huge challenge to realize X-ray flexible imaging technology for real-time monitoring of the curving interface of complex devices. To address these issues, we herein report two isostructural cuprous halides of zero-dimensional (0D) [AEPipz]CuX3·X·H2O (AEPipz = N-aminoethylpiperazine, X = Br and I) with controllable size to nanosize crystal as highly efficient scintillators toward flexible X-ray imaging. These cuprous halides exhibit highly efficient cyan photoluminescence and radioluminescence emissions with the highest quantum yield of 92.1% and light yield of 62,400 photons MeV-1, respectively, surpassing most of the commercially available inorganic scintillators. Meanwhile, the ultralow detection limit of 95.7 nGyair s-1 was far below the X-ray dose required for diagnosis (5.5 μGyair s-1). More significantly, the flexible film is facilely assembled with excellent foldability and high crack resistance, which further acts as a scintillation screen achieving a high spatial resolution of 17.4 lp mm-1 in X-ray imaging, demonstrating the potential application in wearable radiation radiography. The combined advantages of high light yield, low detection limit, and excellent flexibility promote these 0D cuprous halides as the most promising X-ray scintillators.

Large-Area Transparent Antimony-Based Perovskite Glass for High-Resolution X-ray Imaging

Nonlead low-dimensional halide perovskites attract considerable attention as X-ray scintillators. However, most scintillation screens exhibit pronounced light scattering, which detrimentally reduces the quality of X-ray imaging. Herein, we employed a simple and straightforward solvent-free melt-quenching method to fabricate a large-area zero-dimension (0D) antimony-based perovskite transparent medium, namely (C20H20P)2SbCl5 (C20H20P+ = ethyltriphenylphosphine). The transparency is due to the large steric hindrance of C20H20P+, which hinders the formation of crystals during the quenching process, thus forming a glass with low refractive index and uniform structure. This medium exhibits a high transmittance exceeding 80% in the range of 450-800 nm and shows a large Stokes shift of 245 nm, thereby minimizing light scattering, mitigating self-absorption, and enhancing the clarity of X-ray imaging. Moreover, it exhibits a high radioluminescence light yield of ∼12,535 photons MeV-1 and displays a high X-ray spatial resolution of 30 lp mm-1 owing to its high transparency. This study presents an alternative candidate for achieving high-quality X-ray detection and extends the applicability of transparent perovskite scintillators.

One-Dimensional Copper-Doped Rb2AgI3 with Efficient Sky-Blue Emission as a High-Performance X-ray Scintillator

Scintillators have garnered heightened attention for their diverse applications in medical imaging and security inspection. Nonetheless, commercial scintillators encounter challenges with costly rare-earth metals and toxic elements like thallium (Tl), driving the need for sustainable, cost-effective, and eco-friendly alternatives to meet contemporary X-ray detection demands. This study focuses on exploring the potential of Cu+-doped Rb2AgI3 as an effective metal halide (MH) scintillator. One-dimensional (1D) Rb2AgI3 and Cu+-doped Rb2AgI3 single crystals (SCs) were synthesized by using the conventional temperature-lowering crystallization method. When excited by UV light, Cu+-doped SCs emitted a broad sky-blue light at 490 nm with a high photoluminescence (PL) quantum yield (PLQY) of 76.48%. Remarkably, under X-ray excitation, these Cu+-doped SCs demonstrated an outstanding light yield of 36,293 photons MeV-1, a relatively low detection threshold of 1.022 μGyair s-1, and a rapid scintillation decay time of 465 ns. The prepared translucent scintillation film has good uniformity and flexibility, with a high spatial resolution of 10.2 lp mm-1. These results position Cu+-doped Rb2AgI3 as a leading candidate among promising X-ray scintillators, offering superior scintillation light yield, excellent stability, and nontoxicity.

Mn(II)-Based Metal Halide with Near-Unity Quantum Yield for White LEDs and High-Resolution X-ray Imaging

Metal halides have drawn great interest as luminescent materials and scintillators due to their outstanding optical properties. Exploring new types of phosphors with easy production processes, excellent photophysical properties, high light yields, and environmentally friendly compositions is crucial and quite challenging. Herein, a novel Mn(II)-based metal halide (4-BTP)2MnBr4 was produced using a facile solvent evaporation method, which exhibited a strong green emission peaking at 524 nm from the d-d transition of tetrahedral-coordinated Mn2+ ion and a near-unity quantum yield. The prepared white light-emitting diode device has a wide color gamut of 100.7% NTSC with CIE chromaticity coordinates of (0.32, 0.32). In addition, (4-BTP)2MnBr4 demonstrates excellent characteristics in X-ray scintillation, including a high light yield of 98 000 photons/MeV, a sensitive detection limit of 37.4 nGy/s, excellent resistance to radiation damage, and successful demonstration of X-ray imaging with high resolution at 21.3 lp/mm, revealing the potential for application in diagnostic X-ray medical imaging and industry radiation detection.

Perovskite materials in X-ray detection and imaging: recent progress, challenges, and future prospects

Perovskite materials have attracted significant attention as innovative and efficient X-ray detectors owing to their unique properties compared to traditional X-ray detectors. Herein, chronologically, we present an in-depth analysis of X-ray detection technologies employing organic-inorganic hybrids (OIHs), all-inorganic and lead-free perovskite material-based single crystals (SCs), thin/thick films and wafers. Particularly, this review systematically scrutinizes the advancement of the diverse synthesis methods, structural modifications, and device architectures exploited to enhance the radiation sensing performance. In addition, a critical analysis of the crucial factors affecting the performance of the devices is also provided. Our findings revealed that the improvement from single crystallization techniques dominated the film and wafer growth techniques. The probable reason for this is that SC-based devices display a lower trap density, higher resistivity, large carrier mobility and lifetime compared to film- and wafer-based devices. Ultimately, devices with SCs showed outstanding sensitivity and the lowest detectable dose rate (LDDR). These results are superior to some traditional X-ray detectors such as amorphous selenium and CZT. In addition, the limited performance of film-based devices is attributed to the defect formation in the bulk film, surfaces, and grain boundaries. However, wafer-based devices showed the worst performance because of the formation of voids, which impede the movement of charge carriers. We also observed that by performing structural modification, various research groups achieved high-performance devices together with stability. Finally, by fusing the findings from diverse research works, we provide a valuable resource for researchers in the field of X-ray detection, imaging and materials science. Ultimately, this review will serve as a roadmap for directing the difficulties associated with perovskite materials in X-ray detection and imaging, proposing insights into the recent status, challenges, and promising directions for future research.